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Taking the
Mystery out of White Line Disease. (Download
PDF)
By Dr. Richard Shakalis & Dr.
John Pautienis
Researchers have spent a great deal
of time trying to find the single organism that causes the
destruction of hoof wall at the stratum medium, referred to
as white line disease. The hope is that the discovery of the
elusive bacteria or fungus will result in a definitive cure.
Unfortunately, this approach is too simplistic for the complex
biological event that is actually taking place. White line
disease is caused by two different types of opportunistic microorganisms
that exist in a symbiotic relationship. Together they produce
enzymes and exotoxins that break down the protein and collagen
of the hoof wall. This dynamic colony of microorganisms consists
of at least one type of destructive bacteria and at least one
fungus.
This information explains quite a bit.
First, because it is not caused by a single organism, white
line disease may appear different from horse to horse, depending
on the particular makeup of the colony of microorganisms present.
For example, if there is a very aggressive fungus present mixed
in with a virulent bacterium, a fast-growing, hard-to-treat
case will result. Conversely, if a slow-growing, less invasive
fungus is paired with a more benign bacterium, this case can
be treated more easily. There may be two or more destructive
bacteria or fungi present in the same hoof. You can begin to
understand that an infinite number of combinations can result.
This also explains why a certain treatment may work effectively
in one case and fail miserably on the next. To add another
variable to the mix, these colonies are dynamic and grow faster
when the environment is wet and warm, and slower when it is
cold and dry.
In white line disease, bacteria and
fungi live within the confines of the hoof wall in a symbiotic
relationship. That is, they can live independently, but mutually
benefit by each other's presence. Each organism breaks down
the hoof in a different manner while providing metabolites
for the other. The fungi can be heterotrophs, obtaining their
food from nonliving organic matter, or saprophytes, feeding
as parasites on living hosts. They become deeply imbedded within
the hoof wall and send out threadlike filaments called hyphae
that absorb nutrients much like roots of a plant. The bacterium
reproduces more quickly by dividing, but the fungus can produce
spores that makes it harder to kill. Treating for bacteria
or fungus alone is useless because when one is eliminated,
the other will continue to grow unabated. You must control
both simultaneously.
These microorganisms are opportunistic
in nature. That is, they ordinarily will not attack perfectly
healthy hoof tissue but will enter into a small crack, nail
hole, or fissure at the white line. These problems commonly
occur at the stratum medium because this is where the horny
laminae interlocks with the sensitive laminae. There is a rich
blood supply here, and wherever blood is present in nature,
there is a possibility of infection. Obviously a quick is an
open invitation for infection. Another one is a case of laminitis
that causes a split in the laminae. Even subclinical cases
of laminitis, although not severe enough to cause lameness,
could result in small tears at the stratum medium. Even bruising
this area can lead to problems. Any trace of dried blood from
the bruise makes a perfect nutrient for growth of these microorganisms.
Be suspicious of any injury in the area of the white line,
however subtle. It is best to treat white line disease aggressively
and early.
Note the probe is pushed up deep into
the hoof wall before more sound hoof structures are
felt. This soft area indicates diseased hoof material.
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Let's examine a typical case
of white line disease found in the Northeast (Figure
1). The colony of organisms found here are unique
to this particular horse and may be entirely different
from the ones you are fighting, but remember what
all cases have in common: there will be at least
one destructive bacteria along with at least one
destructive fungus found in the culture.
We used sterile culture containers
provided free of charge by a commercial medical laboratory
to gather our hoof samples. We scooped out some soft,
diseased hoof material with a clean instrument and
gave the culture container to the laboratory (Figure
2). In our case we wanted to retest the effectiveness
of an over-the-counter product specifically designed
to treat white line disease, as well as identify
all the bacteria and fungus present. The over-the-counter
product we supplied to the laboratory technician
was Sav-A-Hoof Gel by SBS Equine Products.
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The laboratory technicians took the samples
of diseased hoof wall and spread it on a blood agar
plate and then placed it in an incubator. A mixed
culture of organisms, just like what was found in
the hoof, resulted (Figure 3). Each separate colony
was then placed on their own agar plates, some in
the presence of oxygen and some without, and the
fungal samples were placed in small jars. This resulted
in pure cultures for six different bacteria and a
fungus, which were then identified by the technician
(see Table at end of this page).
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Diseased hoof material was removed
deep from within the hoof wall, along the leading
edge of the infected area, and placed in sterile
culture containers. Then these samples went to the
laboratory technicians for analysis.
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Note separate microorganism
colonies growing across the blood agar culture plate
after being removed from the incubator. This plate
provides nutrients for the organisms to grow on. The
anaerobes, including the fungus, were grown in oxygen-free
jars along with a rich growth medium.
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So what did we find from this
mixed bag culture of micro-organisms? We ran the
gamut, as one would expect, from very harmful to
relatively benign bacteria, as well as a stubborn
fungus in our sample. In every case, the over-the-counter
product we tested - Sav-A-Hoof Gel - worked extremely
well at killing both bacteria and fungus (Figures
4 & 5).
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Of the six bacteria present,
Providencia rettgeri, Klebsiella pneumoniae and Bacillus
subtilis, although sometimes pathogenic in man (see
Table on page 91), are not causing much destruction
of hoof wall tissue here. They are simply taking
advantage of a warm, dark environment to thrive in.
The next grouping of bacteria, the Staphylococcus
and Pseudomonas, are capable of producing enzymes
destructive to the hoof wall. The Staphylococcus
prefers blood and can thus elaborate many powerful
toxins and enzymes through the blood.
By far the main destructive
bacteria found was Clostridium difficiles. The Clostridia
found here has some particularly nasty first cousins
that are responsible for tetanus, botulism and gas
gangrene. Clostridium is capable of producing spores
and extra-cellular products such as powerful proteinases
and collagenases, substances very destructive to
the hoof wall. It is an anaerobe, which means it
lives only when there is no oxygen present. It can
produce a whole host of destructive enzymes such
as fibrinolysins, collagenase, lecithinase and cytolysins.
It is one nasty bacteria.
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The bacteria are growing
on the entire agar plate except in the darker, clear
area surrounding the purple Sav-A-Hoof Gel sample.
This area is bacteria free and represents the very
effective kill zone. The bacteria are unable to grow
or survive in this zone.
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The special culture pictured
in the jar isolated the fungus Geotrichum. This fungus
is an aggressive saprophyte that grows vigorously
on organic matter. It is commonly found in sewage
treatment plants and is a spore former, which means
it is difficult to eliminate. As shown in Figure
5, the Sav-A-Hoof Gel effectively killed this fungus,
as well.
The best way to treat white
line disease is first to recognize it early and then
treat it with a product that is a broad-spectrum
bactericide as well as a fungicide. You must remember
that dry, cool conditions are your ally and that
warm, wet ones are your enemy. Because some of the
different organisms present are capable of producing
spores, you must choose a product that is powerful
and stays active for a long time. It takes time and
patience to treat these infections once they gain
a foothold. Even if you don't kill all the organisms
initially, you may kill enough of them to slow the
advancement of the disease to the point that it may
grow out with successive trimmings.
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Note the fungus is unable to grow or
survive within the clear area surrounding the Sav-A-Hoof
Gel sample. Even with ideal growth conditions, with
no oxygen and a rich growth medium, this area is
fungus free and again represents the effective kill
zone.
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VIRULENCE OF ORGANISMS
IN HOOF AND IN MAN
| Organism |
Virulence In Hoof |
Virulence In Man |
| Klebsiella pneumoniae |
Minimal |
Bacterial pneumonia and other localized
infections such as cholecystitis, cholangitis, sinusitis
mastoiditis and meningitis and endocarditis |
| Providencia rettgeri |
Minimal |
Wound infections |
| Bacillis subtilis |
Minimal |
Gastrointestinal infections |
| Staphlylococcus |
Produces powerful enzymes and toxins
that break down blood and fibrin found in the hoof wall |
Pus-producing infections of the skin
and less frequently lungs, kidneys, and bone |
| Pseudomonas |
Produces enzymes that can break down
collagen |
Can cause antibiotic-resistant disease
in persons of weakened resistance |
| Clostridia difficiles |
Powerful enzymes break down protein
and collagen of the hoof wall |
Can produce extremly potent exotoxins,
Examples of Clostridialm infections in man: tetanus, botulism
and gas gangrene |
| Geotrichum (Fungus) |
Breaks down hoof wall already damaged
by bacterial enzymes |
Geotrichosis - an acute, subacute
or chronic disease that enters oral cavity or lung, resulting
in a chronic cough and bronchitis |
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